Johansson J, Nilsson G, Strömberg R, Robertson B, Jörnvall H, Curstedt T
Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden.
Biochem J. 1995 Apr 15;307 ( Pt 2)(Pt 2):535-41. doi: 10.1042/bj3070535.
Native pulmonary-surfactant-associated lipopolypeptide SP-C, its chemically depalmitoylated form and several synthetic analogues lacking the palmitoylcysteine residues were analysed for secondary structure in phospholipid micelles and for biophysical activity in 1,2-dipalmitoyl-sn-glycero-3- phosphocholine/phosphatidylglycerol/palmitic acid (68:22:9, by wt.). Compared with the native molecule, with the entire poly-valyl part in a known alpha-helical conformation, depalmitoylated SP-C was found to be still mainly alpha-helical, but with an approx. 20% decrease in the helical content. A synthetic hybrid polypeptide where the entire poly-valyl alpha-helical part of native SP-C had been replaced with the amino acid sequence of a transmembrane helix of bacteriorhodopsin is also predominantly alpha-helical. In contrast, synthetic SP-C analogues lacking only the palmitoyl groups, by replacement of the palmitoylcysteine residues with cysteine, phenylalanine or serine, or lacking the positively charged amino acids by replacement with alanine, are considerably less alpha-helical than both native and depalmitoylated SP-C. The data indicate that the SP-C palmitoyl groups are important for maintenance of the alpha-helical conformation in parts of the polypeptide, and that the poly-valyl alpha-helical conformation is not fully formed in synthetic SP-C polypeptides. Furthermore, the helical structure of both native and depalmitoylated SP-C in dodecylphosphocholine micelles is very resistant to thermal denaturation, exhibiting ordered structure at 90 degrees C. The alpha-helical content grossly parallels the peptide-induced acceleration of the spreading of phospholipids at an air/water interface and the increase of surface pressure. The data suggest that the alpha-helical conformation itself, rather than just the covalent structure, is of prime importance for the biological function of synthetic pulmonary-surfactant peptides.
对天然肺表面活性物质相关脂多肽SP - C、其化学脱棕榈酰化形式以及几种缺乏棕榈酰半胱氨酸残基的合成类似物进行了分析，以研究它们在磷脂微团中的二级结构以及在1,2 - 二棕榈酰 - sn - 甘油 - 3 - 磷酸胆碱/磷脂酰甘油/棕榈酸（重量比为68:22:9）中的生物物理活性。与天然分子相比，其整个聚缬氨酸部分呈已知的α - 螺旋构象，发现脱棕榈酰化的SP - C仍主要为α - 螺旋结构，但螺旋含量约降低20%。一种合成杂合多肽，其中天然SP - C的整个聚缬氨酸α - 螺旋部分已被细菌视紫红质跨膜螺旋的氨基酸序列所取代，该杂合多肽也主要为α - 螺旋结构。相反，仅通过用半胱氨酸、苯丙氨酸或丝氨酸取代棕榈酰半胱氨酸残基而缺乏棕榈酰基团的合成SP - C类似物，或者通过用丙氨酸取代而缺乏带正电荷氨基酸的合成SP - C类似物，其α - 螺旋程度明显低于天然和脱棕榈酰化的SP - C。数据表明，SP - C的棕榈酰基团对于维持多肽部分的α - 螺旋构象很重要，并且在合成SP - C多肽中聚缬氨酸α - 螺旋构象未完全形成。此外，天然和脱棕榈酰化的SP - C在十二烷基磷酸胆碱微团中的螺旋结构对热变性具有很强的抗性，在90℃时仍呈现有序结构。α - 螺旋含量与肽诱导的磷脂在气/水界面铺展加速以及表面压力增加大致平行。数据表明，α - 螺旋构象本身而非仅仅共价结构对于合成肺表面活性肽的生物学功能至关重要。
